Natural Gas Pipelines

The Department of Transportation is responsible for ensuring the safety of about 267,000 miles of interstate natural gas pipelines. The use of an instrumented internal inspection device known as a "smart pig" is the only way to detect internal and external corrosion without excavating the pipe. Pipeline corrosion is the second leading cause of pipeline accidents after accidental excavation damage. Smart pigs can also spot other flaws, such as gouges and dents, that weaken a pipe's structural integrity. Smart pigs have their limits, however. They cannot detect defects like longitudinal cracks and metal loss in pipe welds, and some pipelines with sharp bends and other configurations cannot accommodate smart pigs. Even so, this technology has the potential to greatly reduce pipeline accidents. No federal regulations governing smart pigs or the frequency of smart pig inspections are on the books. Because corrosion can lead to ruptures and leakages in aging pipelines--problems that smart pigs can avert--GAO urges DOT to complete the feasibility study and regulations mandated under the law.

GAO found that: (1) DOT is responsible for developing, issuing, and enforcing natural gas transmission pipeline safety regulations; (2) from 1985 to 1991, natural gas pipeline incidents totalled 1,726, involving 131 fatalities and 634 injuries; (3) causes for pipeline failure include outside-force damage, corrosion, and defective materials; (4) smart pig inspections have the potential to detect internal and external corrosion, provide information on metal integrity, and detect other pipeline flaws, without pipeline excavation; (5) companies use smart pigs to determine the source and location of internal or external pipe problems, locate anomalies, and establish existing pipeline conditions; (6) smart pig use enables companies to minimize pipeline downtime, plan effective maintenance, ensure operational safety, and perform condition appraisals prior to pipeline sales; (7) smart pigs' operational limitations include their inability to negotiate sharp bends, detect longitudinal cracks, and locate potential pipe seam failures and circumferential weld metal loss; (8) the cost of using smart pigs depends on the pig type, pipeline diameter, pipeline cleanliness, pipeline length, pig vendor competition, amount of corrosion, amount of excavation needed, and extent of data interpretation required; (9) the two types of magnetic-flux smart pig technologies are first-generation, which is about 25 years old, and the more recent second generation, which has advanced capabilities for flaw detection; (10) RSPA has not completed the legislative requirements to improve pipeline safety, including a study discussing smart pig requirements and mandatory regulations requiring new and replacement pipelines to be capable of accommodating smart pigs; (11) companies do not use smart pigs frequently because of a lack of federal regulations; and (12) pending legislation would initiate regulations and require smart pig inspections in densely populated areas.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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